1. Field of the Invention
The invention generally relates to a fuel injector and, more particularly, to a fuel injector having a piezoelectric actuator that provides improved rate shaping qualities and improved multiple control of the fuel injection events of the fuel injector and a method of use thereof.
2. Background Description
There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a control valve body may be provided with two, three or four way valve systems, each having grooves or orifices which allow fluid communication between working ports, high pressure ports and venting or drain ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid that is capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
In current designs, a control valve controls the flow of working fluid from the oil rail to the intensifier chamber and hence the intensifier piston (i.e., fill position), as well as controls the flow of the working fluid from the intensifier chamber to ambient (i.e., drain position). During an injection cycle, fuel in a high-pressure chamber is placed under pressure by the intensifier piston. The high-pressure fuel will flow to the nozzle assembly where it will overcome spring forces and other hydraulic forces to lift the needle for injection of fuel into a combustion chamber.
However, simply using this type of fuel injector and the accompanying multiple process may not be adequate to reduce emissions or provide varying quantities of fuel (e.g., pilot quantity of fuel) during the combustion process. Accordingly, many types of fuel injectors have been designed which attempt to reduce emissions, from providing a pilot quantity of fuel and multiple injections to other controls. In one type of system, a piezoelectric actuator is used to control an injection cycle. For example, a piezoelectric actuator is operable to control the fuel pressure within a control chamber defined, in part, by a surface of the valve needle of the injector. This is referred to as a parasitic escape of fuel. Further, during injection, pressure waves may be transmitted along the fuel passages and lines which, in turn, may give rise to undesirable needle movement during injection and may be of sufficient magnitude to cause secondary injections. The large control chamber may cause this shortcoming.
In other known systems, additional valves, such as three way poppet valve are required in order to provide a positive fuel pressure within the control chamber. The three-way valve, in general, will control the injection cycle of the fuel injector. Being more specific, the three way valve will provide (i) fuel into the control chamber in order provide a pressure therein and maintain the needle valve in a closed position, (ii) drain the fuel from the control chamber to a drain supply line and (iii) provide fluid communication between the control chamber and the high pressure fuel line. In this manner, control of the needle valve can be maintained. These three way valves are typically spring loaded and controlled by an actuator. In this same type of system, an electronically controlled valve is required in order to allow the fuel to enter the high-pressure fuel chamber from a low-pressure fuel supply line. This electronically controlled valve is typically in the open position to allow the fuel to enter the high-pressure fuel chamber, but also allows for “bleeding” (i.e., fuel to flow from the high-pressure chamber to the low pressure supply line). To close this valve, a controller or solenoid closes the valve so that the intensifier piston can provide a high-pressure environment which, initially, will not open the needle valve due to various other counter forces such as, for example, the fuel pressure within the control chamber.
The invention is directed to overcoming one or more of the problems as set forth above.